Accelerometer



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5 Sheets-Sheet 1 Feb. 18, 1941. J. E. sHRADER ACGELEROMETE R Filed Nov. 17, 1958 3 Shoots-Shut 2 Feb 18, 1941 J. E; sHRADr-:R 2,231,957

ACCELEROMETE R Filed NOV. 17, 1958 3 SheBtS-Sheet 3 Patented Feb. `18, 1941 UNITED STATES PATENT OFFICE ACCELEROMETER James Edmond Shrader, Drexel Hill, Pa.

Application November 17, 1938, Serial N o. 240,905

6 Claims.

This invention relates to accelerometers and more particularly to an instrument of this type for observing, measuring and recording three simultaneous components of acceleration.

It is an object of the present invention to provide an accelerometer which will be capable of measuring v1. 'brations of high frequency.

It is a further object of the present invention to provide an accelerometer wherein a high degree of sensitivity is provided and which will have a natural frequency above that of the accelerated body under test.

It is a further object of the present invention to provide an accelerometer in which a large magnification of the motions of the pendulums may be provided.

It is a further object of the present invention to provide an accelerometer having improved structure for damping and suppressing free vibration of the pendulums employed therein.

It is a further object of thepresent invention to provide an accelerometer in which the three components of acceleration in planes each at right angles to the others are simultaneously determined.

It is a further object of the present invention to provide an accelerometer particularly adapted for three components of acceleration and in which a visual indication may be obtained at the same time that quantitative readings are recorded.

It is a further object of the present invention to provide a portablethree component accelerometer 4which will be sturdy and reliable.

Other objects of the invention will appear from the annexed specification and claims.

The nature and characteristic features of the invention will be more readily understood from the following description, taken in connection with the accompanying drawings forming part hereof, in which:

Figure 1 is a horizontal section of an accelerometer embodying the main features of the invention, certain of the interior parts being illustrated in plan and other parts being removed for clarity of illustration;

Fig. 2 is a vertical section thereof, taken approximately on the line 2--2 of Fig. l, certain of the interior parts being shown in side elevation;

Fig. 3 is a similar view taken in a transverse direction; and

Fig. 4 is an enlarged view, partly in plan and partly in horizontal section, illustrating certain details of construction.

It will, of course, be understood that the description and drawings herein contained are illustrative merely, and that various modifications and changes may be made in the structure disclosed without departing from the spirit of the invention.

' Referring more particularly to the drawings, the accelerometer there illustrated includes an outer casing I having a lower portion within which the acceleration responsive elements are mounted and an upper portion I'I, removable from the lower portion l0, within which photographic recording structure is. provided.

In the lower portion of the casing I0 a base I2 is provided which is preferably of cast aluminum or similar material and has supports I3, I4 and I5 extending upwardly therefrom.

Three pendulums IBa, I6b and I6c are provided, operative respectively in planes at right angles to each other, and each of the pendulums with its damping and indicatingA structure is substantially the same in the details of its construction. Each pendulum preferably includes a thin relatively stiff strip of phosphor-bronze or other suitable material.

The support I3 has the cantilever pendulum' Ia mounted on an upper edge thereof in any suitable manner, bolts Il being' satisfactory for this purpose. The pendulum I6ais preferably mounted with the plane of the stripdisposed in a horizontal position so that it is free to vibrate in a vertical direction, as hereinafter more fully referred to. The support I3 also has secured to the side face thereof another cantilever vpendulum I6b which is similarvto the pendulum Ilia and is mounted with its plane vertically disposed so that it may vibrate in a horizontal direction.

VThe upright I4 preferably has mounted on a side edge thereof another cantilever pendulum IBc which is similar to the pendulum I6a and is mounted inta vertical plane so that it may vibrate in a horizontal direction at right angles to the direction of vibration of the pendulum Ib.

The natural frequency of each of the pendulums may be and preferably is high so that if desired, the pendulums Ilia, |619 and I 6c may follow the motions of the accelerated body as to which information is desired. The pendulums are preferably selected and proportioned so that the natural frequency is above that of the accelerated body to be observed and therefore above the range of resonance.

The pendulum strips are each very. light and fairly stiff. Each strip is preferably provided on one side thereof with a boss I8 having an internally threaded portion I9 within which a stud 20 is mounted. Each pendulum IBa, I6b and I6c tritt is also preferably provided on the face opposite the boss I8 with a small plate 2| which may be secured thereto by rivets 22.

Weights are mounted at the outer or free end of each of the pendulum strips I6a, I6b and |60 remote from the xed end, to provide the proper mass and preferably consists of a plurality of nuts 23 mounted on the threaded stud 20.

A hole 24 drilled partly in the pendulum strip and partly `in the platerZAI is providedvfonthe ireception4 9i, 2.1.11 sdillstipin 25 lffs'iensllfl' gagement in the hole 24, the nuts 23 permitting the increasing of the frictional grip on the pin. for holding the pins 25 in the adjusted positiorf' I6b and 16e 'isi-.-

Each of the pendulums I6a, damped and for this purpose air damping devices have been found most sutablebecause of their compactness, light weight, and reliability within the atmospheric temperature ranges.

The construction of the air damping devices is shown in detail in Fig. 4.. Each-0f the air dampingI devices preferably comprises a pair of hollow disks' 30 having the walls -thereof of thin elastic metal united at the outer edges to providea hollowinterior chamber 3I. The boss I8 is secured4 to one of the disks ,30"and the other disk -preferably has aplug -32 secured thereto, the plug .32. being carried in one ofthe uprights, as for example I4. The. plug 32-has a central aperture 33` therethrough in communication withv the hollow interior chamber 3I. v

' An adjustable needle valve 34 is provided which includes, a threaded stem-mountediwithin a co1- lar 35 which is also mounted in the support I4. The stem has a conicallend portion 36 seating inl-the plug 32.. lA plurality of .apertures 31 are provided through the collar 35 for providing communication between the aperture 33 and the atmosphere in accordancel with the vsetting of the valve stem 34.: A lock nut 38 is vpreferably provided'for locking thevalve stem 34 in thev desired adjusted position.`

The air damping device for the pendulum Ib is preferably secured to the upright I4 and an opening -4I) may be provided-in the casing wall for accessto the valve stem". `The air damping device for the pendulum I6a is preferably se# cured to the vbase vI2V and an opening 4I is provided through the base I2 and the bottom casing wallffor access .to the valve'stem 34 for purposes of adjustment. The air damping device for the pendulum I6c is `preferably secured to the upright I5 and an opening 42 may be provided through theV side casing wall for access to the valve stem 34, for adjustment of the' damping effect. When the pendulums I6a, I6bv and |60 are actuated, as hereinafter more fully referred to, air is drawn into and forced out ofthe chambers 3I by the movement-of the pendulums. The energy mi of the vibrating'pendulumsis thus dissipated to o f the deflections of the pendulums 16d, I6b and 755e Ijc during vibration Iso that-the respective come` ...Which form part of the base I2. The spindle 45 -4Vhas mounted thereon a small concave mirror 4'I.

'1 Each of the pins 25 on the pendulums I6a, |612 and .I 6c preferably has end portions of a piece of phosphor-bronze wire secured thereto, the Wire having parallel. portions 48 extending to the spindle 45 and being wrapped therearound and extending= through small apertures 49 in the spindle 45 and -then as-at 50v to a small triangular plate 5I through which the Awire is looped. A spring'52 is secured ,to lthe triangular plate 5I, the other end of the spring 52 being mounted on a `suitable support carried byor on the base I2. It will `be seenl that by `adjustment of the pin 25, the 2mirrors v4l may bev brought lto the proper position. It `willbe noted that the movementofthe pendulums isvtranslated by the ,connecting wires,48 ,.andl tends to impart a rotary oscillatory movement` to the spindle 45 in accordi-- ance with the movement of the respective pendu-vv lums I6a,.-Ifb` andl I6c and. againstthe biasing imparted by the springs 52 to the spindles. 45.

vided with similar structure. An electric lamp 66a., preferably enclosediin' a housing qopen'atA the bottom, and underthe control'of the rheostat 64 is removably mounted in the topwall of .the casing I0. lIhe lampv preferablyhas a longv filament 66h and .provides a sourcefor beams of light so that a beam may be reflected byvthegmirrors; 4'I,for the purpose of giving a,visual indication' andl afrecorded indication, as hereinafter pointed out.

`In order thatthe light from the filament 66D offtheelectric lamp a, may reach the mirror 4'I;onthe spindle 45 .operated from *the pendulum. |603 a .right angled prism BI is provided and is carried by a `suitable vadjustable mounting 62. The beam of :light to and from this mirror 4l will thus be brought into `a location-adjacent the reflections of the other-mirrors, the image of the mirror being indicatedat 41a `(Fig. 1).

The upper wall. ofthe casing lil-has a slot 63 therethrough to which "thebeams of light from the'th'ree mirrors v4'I:.are directed'and the upper portion of-xwhich-:is incommunication with the photographiczxrecording .structure within the casing portion II.

The casing-Il). is also provided with a viewing opening as at 65".-Witha ground glass plate 66, supported-by brackets 6"I, covering the opening 65. TheA ground-,glass plate :66 may, if desired; have suitable graduations thereon. L

VA plane mirrorl`68 -iscarried by av bracket 69 secured to the upper part of the casing I0 forV reflecting the beams 'of lightfr'om the mirrors 4'Irefiected thereon. to the viewing opening 65.

`Suitable photographic recording structure,` the details of which form no part of the present in- Yention, is preferably provided in the upper casing portion I I and includes film rolls 'I0 driven by a suitable-train of gearingfII, and preferablyv at predetermined Variable speeds from kan electric motor 'I2 mounted within the casing ID.

A shutter 13 is provided between the photographic recording structure and the casing portion I I so that when the instrument is not in use, the film will not be exposed to the interior of the instrument.

The operation of the accelerometer of the present invention will be clear from the foregoing.

With the lamp 60a illuminated under the control of the rheostat 64 to the desired brilliance, the instrument is ready for use. If it is desired to record the vibrations, the motor is operated to drive the lm in the photographic recording casing Il, the desired selection of speed being made by the operator.

Upon the vibration of one or more of the pendulums la, I6b and |60 in accordance with the plane of the inducing acceleration, the movement of the respective pendulums Ilia, |6b and I6c will be translated andthe moving beams of light from the lament 60h of the lamp striking the respective mirrors 41 will be reflected to the slot 63, and the movements may be simultaneously viewed at the opening 65 to which the beams are carried by the mirror 68. Since the movements of the pendulums lBa, Ib and |6c are all similarly transmitted, simultaneous readings of acceleration in the three component directions may be observed and recorded.

I claim:

1. An accelerometer including an acceleration responsive member movable in a single predetermined plane, a iiXed abutment having a portion extending transversely with respect to said plane, and a compressible damping device interposed between said member and said abutment and operable by said member for damping vibrations of said member, said damping device including a flexible metallic chamber device having the interior thereof in restricted communication with the atmosphere.

2. An accelerometer including an acceleration responsive member movable in a single predetermined plane, a iixed support and a damping device interposed between said member and said support and operable by said member for damping vibrations of said member, said damping device including a flexible contractible and expansible hollow metallic chamber mechanism having a conduit for communication with the atmosphere, and means for varying the uid flow through said conduit.

3. An accelerometer including an acceleration responsive member mounted for movement in a single predetermined plane, a damping device operable by said member for damping vibrations of the member, said damping device including an elastic contractible and expansible chamber mechanism having a conduit for communication with the atmosphere, and valve means in said conduit for controlling the iiuid ilow through said conduit.

4. An accelerometer including a frame, an acceleration responsive member mounted in said frame for movementI in a single predetermined plane, and a damping device secured to said frame and operable directly by said member for damping vibrations of the member, said damping device including a flexible hollow metallic capsule provided with a conduit for communication with the atmosphere, and valve means for controlling the fluid flow through said conduit.

5. An accelerometer including a frame, an acceleration responsive member mounted in said frame for movement in a single predetermined plane, and a damping device connected to said member, said damping device having a portion fixedly mounted in a portion of said frame, said damping device including a exible metallic capsule connected on one side thereof to said member and on the other side thereof to said ixedly mounted portion, and provided with a conduit for communication with the atmosphere, and adjustable valve means for controlling the fluid flow through said conduit.

6. An accelerometer including a frame, an acceleration responsive member mounted in said frame for movement in a single predetermined plane, weights adjustably secured to said member, and a damping device connected to said member, said damping device having a portion xedly mounted in a portion of said frame, said damping device including a flexible metallic capsule connected on one side thereof to said member and on the other side thereof to said xedly mounted portion and provided with a conduit in continuous communication with the atmosphere, and adjustable valve means for controlling the fluid ow through said conduit.

JAMES EDMOND SHRADER. 

